Control regulators or throttling valves of the type incorporating deformable elastomeric diaphragms or liners, that operate by pressure differentials on their two sides to variably uncover a plurality of orifices, e.g., slots, in a baffle positioned between an upstream inlet and a downstream outlet in a flowpath, are well known in the art. The operating pressure is referred to as a pilot pressure and is changeable to control the operating position of the diaphragm. Such valves may, for example, be used for controlling the flow of a variety of fluids and gases and, because of their regulating nature, are often operated in a partially open position with a substantial differential between the upstream and downstream pressures. While such valves have, in general, rendered satisfactory service, they are not without problems. In gas applications in particular, the flow velocity may create icing conditions on the diaphragm and give rise to problems in shut-off.
The flexible diaphragms are also subject to stretching. Under certain operating conditions the diaphragms may be "pinched" or folded over upon themselves, a condition which is detrimental to the life of the diaphragm and proper functioning of the valve.
The baffle generally comprises a frustroconical shaped grill containing slot-like apertures that are progressively covered and uncovered by the diaphragm as it is "rolled" inot and out of contact therewith. The portions of the slots that are uncovered by the diaphragm determine the flow rate through the baffle. Difficulties in some designs have resulted from uneven rolling of the diaphragm. A backup "nose piece" is often included to provide a stationary surface against which the diaphragm may rest to assist in controlling its movement during unrolling to minimize the above mentioned pinching and foldover. The slot configuration for the grill holes is very common, although circular or other shaped grill holes may also be used.
Another problem encountered with the rolling diaphragm is its tendency to be extruded into the slots of the frustroconical grill, by action of the operating pilot pressure against the diaphragm, when the valve is closed or partially closed. Another notable deficiency is the lack of any readily available means for indicating the amount that the valve is open for flow. Also, the valves are generally cylindrically shaped and designed to be clamped in a pipeline by suitable flanges and bolting, which has rendered servicing of the valve inconvenient in many installations.
The control regulator described and claimed in the referenced copending application provides a solution to the above mentioned difficulties in prior art devices. That control regulator includes a movable nose piece and a substantially nonstretchable diaphragm that, in a preferred embodiment, is fabric reinforced. The results obtained with the regulator have been very good at temperatures up to 120.degree. F. and pressures up to 750 pounds per square inch (psi).
It has been found, however, that blistering of the diaphragm sometimes occurs when the control regulator is used in applications in a natural gas flowpath where the temperature of the gas reaches 150.degree. F. at pressures of 750 psi. The blistering, generally found in the downstream side of the liner, is manifested by a separation of the downstream rubber or elastomer from the fabric and is believed to be due to entrained gas that permeates the rubber material of the diaphragm and forms pockets adjacent to the fabric reinforcement. The blistering seems to occur more readily at higher temperatures, probably as a result of the higher energy level of the gas molecules and the increased softness of the diaphragm. The present invention provides a solution to this problem by enabling release of entrained gases from the diaphragm.